Flow sensors measure the quantity or rate of fluid flowing through a given cross-sectional area over a given time interval. In particular, a two phase flow sensor measures the quantity or rate of fluid flow for a fluid mixture that includes two different phase components (e.g., gas/liquid, liquid/solid, solid/gas, etc.). Examples of two phase flow measurements include, but are not limited to: bubble flow, wavy flow, slug flow, annular flow, and slurry flow.
Two phase flow measurements have widespread applications in many industries, including the semiconductor industry. For the semiconductor industry, in particular, the measurement of slurry flow is an area of particular interest. A slurry is a specialized solution that contains free abrasives, and is used for chemical-mechanical polishing of wafers. An accurate flow measurement is necessary for control of slurry flow.
When the flowing medium contains more than one phase component, a gas and a liquid by way of example, the gas-to-liquid ratio may be unknown, and may change slowly over time. In this case, an exact knowledge of the mixing ratio and the properties of the components of the fluid mixture is needed. However, at present there is a lack of flow sensors that can dynamically incorporate the properties of the components of a multi-component fluid mixture, for two phase flow. Using conventional flow sensors, it is necessary to perform separate calibrations each time the ratio of the phases in the fluid mixture changes.
It is therefore desirable to provide a method and system for measuring two phase flow that allows the ratio of the different constituent phases in the fluid mixture to be determined, thereby allowing for an accurate measurement of the two phase flow rate.